1. Field of the Invention
The present invention relates to a device and method for the electrolytic treatment of liquids, particularly for the electrolytic treatment of aqueous-based waste streams to cause impurities in the waste stream to coagulate or otherwise precipitate out of the waste stream.
2. Description of Related Art
It is known to electrolytically treat liquids, such as aqueous-based solutions, to cause impurities to coagulate or otherwise precipitate from the solution. In such a treatment method, an electric field is applied to a liquid contained in a treatment chamber in order to precipitate impurities. In some of these devices, the electrodes are metal tubes or pipes, as is disclosed in U.S. Pat. No. 4,293,400 by Liggett and U.S. Pat. No. 4,872,959 by Herbst et al. It has been found that at least about three hours are required to repair or replace the electrode tubes in the concentric tube design disclosed in these patents. This amount of down time is unacceptable for most commercial applications.
U.S. Pat. No. 5,043,050 by Herbst discloses a device in which the electrodes are flat. However, when this particular device is placed in a high volume treatment facility, it is difficult to adequately seal the edges of the unit, particularly after long periods of use. Moreover, uneven liquid flow between the electrodes can produce plugging on the side with the lower flow rate, possibly forming a resistive bridge of the plugged material which causes heat build-up and malfunction of the treatment unit.
Various other designs have been proposed for electrolytic treatment units. U.S. Pat. No. 5,271,814 by Metzler discloses a thin film electrocoagulation apparatus that utilizes a cascading path among electrodes for the treatment of liquids. However, it is difficult to maintain adequate flow velocity within this cascade-type structure. Inadequate flow velocity leads to plugging of the contaminant material, as is discussed above. Further, thin film devices do not supply sufficient current to the waste stream to form the most stable, and therefore most desirable, precipitate compounds. Thin film electrocoagulation devices operate by forming a film of contaminant on the electrode plates and passing the current through that film. It is not possible to reverse the electrode polarity in a thin film device since a polarity reversal will destroy the film.
U.S. Pat. No. 3,925,176 by Okert discloses an apparatus for the treatment of sewage that includes an electrolytic treatment device. The device comprises a plurality of electrode plates around which the liquid sewage to be treated is passed. However, the design of the treatment chamber disclosed by Okert is susceptible to plugging. Further, the electrode plates are not easily, nor individually, removable from the treatment chamber for replacement and the plates cannot be powered in a series electrical connection, which is desirable for many applications.
U.S. Pat. No. 3,679,556 by Doevenspeck discloses an apparatus for treating liquids, such as for the pasteurization and sterilization of beer. The apparatus includes a cascade container of positive and negative carbon electrodes. An induction coil is connected to the container on the upstream side. However, this device has many of the same drawbacks as the Okert device discussed above.
It would be advantageous to provide an electrolytic treatment device for treating liquid waste streams which could operate in an efficient and economical manner. It would be particularly advantageous if the electrodes could be easily removed for replacement. It would be advantageous if the device was not susceptible to plugging. It would be advantageous if the electrodes in the device could be easily switched from a series electrical connection to a parallel electrical connection.